This was a strange story, even for 1966. A prominent scientist specializing in miniaturization is in a coma due to a blood clot. The crew of a submarine is miniaturized and injected into his bloodstream to get the clot. Bad things happen before it’s all over, including Donald Pleasance getting eaten by a white blood cell. It had the makings of a really bad B movie, but it had a script co-written by Star Trek writer Jerome Bixby, state-of-the-art special effects for 1966 (some foreshadowing 2001), a novelization by Isaac Asimov, and Raquel Welch, just in case any of that bored you.